The Olympic silver medallist Lizzie Armitstead has withdrawn from the Great Britain team for the world championship road race on Saturday due to illness. The 23-year-old from Otley won Britain's first medal of the London 2012 Olympics in the road race and was poised to lead the team in the 129km race in Limburg, the Netherlands.

A statement from British Cycling read: "Lizzie Armitstead has withdrawn from the UCI Road World Championships on Saturday due to illness. The team have decided not to call in a reserve rider at this stage."

Germany's Tony Martin, meanwhile, successfully defended his men's time-trial title with a narrow win over Taylor Phinney of the United States.

Martin, the Olympic silver medallist behind Bradley Wiggins, completed the winding and hilly 45.7km route in 58min 38.76sec to claim Germany's second victory after Judith Arndt won the elite women's event on Tuesday. Wiggins, who will start Sunday's road race, and the four-time time-trial champion Fabian Cancellara, who failed to recover from a shoulder injury, were both missing.

"After all the ups and downs this season, it's a super-nice finish now," said Martin, who fell and broke a wrist on the first stage of the Tour de France. "Taylor was more amazing because everyone knew that I am strong but not so many people knew about Taylor."

Phinney finished just over five seconds behind in 58.44.13, with bronze going to Vasil Kiryienka of Belarus in 1hr 23.75sec.

Alex Dowsett, Britain's sole representative in the absence of Wiggins and Chris Froome, finished eighth in 1hr 1min 4.82sec, with Spain's Alberto Contador ninth. Contador, the Vuelta a España champion, was the penultimate rider to take to the course, two minutes ahead of Martin, but was overtaken by the German after around two-thirds of the route. "I was really surprised because I really thought that he would be one of the strongest contenders today for the title," Martin said.

Phinney was four seconds faster than Martin at the first time check, but the German moved 13sec ahead at the second.

At 38.4km, Martin held an eight-second advantage over Phinney, meaning the finishing ascent of the Cauberg would determine the winner.

Phinney had Sweden's Fredrik Kessiakoff, who started two minutes ahead of him, in his sights in the latter stages, giving him a target to chase, and looked like he might snatch victory on the brutal climb. The American was fourth in the road race and time-trial at the London Olympics, but ensured he would take a medal by finishing provisionally first with only Martin and Contador, who was out of contention and faced the embarrassment of being overtaken by Martin after 30km, behind him on the road.

The question was the colour of the medal but Martin had just enough energy left on the Cauberg to retain the rainbow jersey he won in Copenhagen 12 months ago. "Even the last 200m were so long because we had a full headwind on top of the Cauberg," Martin said. "It was really, really hard."